... sometimes system hang up

Hi,

I try to run Suse Linux 7.1. on a NETRA I as firewall. It is only a
minimum system (without X) and all the hardware works fine, but
sometimes the system hang up. Nothing goes: No console and stop-a
doesn't work, too. It is possible, that the system is not stable or
there is a problem with ipchains (ipchains -L is very slow)
??????????????

NETRA I (sun4m)
Linux 7.1. sparc (several update-pachtes and update kernel 2.2.19)
hme-ethernet and quad-ethernet works
Installation Minimum System

Thanx for help.
Stephan.